Opposition Leader Bill Shorten has labelled a royal commission into union corruption a political witch-hunt, while warning he would take a zero-tolerance approach to union corruption.

In his first public comments since a Fairfax Media investigation uncovered revelations of corruption and links between the construction union and organised crime, Mr Shorten suggested the Abbott government had undermined the work of law enforcement agencies by pushing for a royal commission.

The Abbott government promised before the election to launch a judicial inquiry into the Australian Workers Union slush fund affair but is now poised to launch a royal commission with sweeping powers that will probe more broadly into the use of slush funds.

Mr Shorten brushed aside suggestions that Labor was too close to unions such as the CFMEU, which is at the centre of the revelations, and which donated $618,398 to the Australian Labor Party in the 2012-13 financial year.

Employment Minister Eric Abetz said Mr Shorten must distance himself from the CFMEU by refusing its funding. He said the union had given Labor more than $5 million in donations since 2007-08. ''Labor is hopelessly conflicted on CFMEU donations,'' Senator Abetz said. ''Never before have the interests of the union bosses been so different from those of union members.''

Mr Shorten said: ''When we talk about election donations, why don't you ask me about the money being given by big tobacco to the Liberal Party?

''No one, it doesn't matter who you are, can support corruption for breaking the law … there should be zero tolerance of any criminal activity, in trade unions or corporate Australia,'' he said.

On Monday, the Australian Electoral Commission published the 2012-13 annual financial returns from political parties and donors, showing Labor's total revenue was $54.7 million last year.

Total receipts declared by all ALP branches, including from the federal branch, was $33,512,267.

Of the receipts that were declared, unions contributed $5,418,419 to the party through donations and other payments.

The Shop, Distributive and Allied Employees Union gave the most to the Labor Party, handing over a declared $1,219,057.

The Australia Manufacturers Workers Union was next, at $749,626, followed by United Voice ($674,737), the CFMEU ($618,398) and the AWU ($599,235).

The Victorian Labor Party also reaped $3.65 million from the sale of some of its property holdings to little-known Chinese investor Zhongfu Investments. ''It's not a donation, it's a transaction,'' said ALP state secretary Noah Carroll.

According to AEC figures, the Liberal Party's total revenue was $73.1 million last year, compared with Labor's $54.7 million. The Nationals bolstered the Coalition's haul with $8.3 million, while the Greens received $8.1 million in revenue.